The former Leicester City man had a point to prove in the lunchtime kickoff after being left out of the England squad for their UEFA Nations League matches against Greece and Finland this month.
Maddison fashioned numerous chances for his teammates in the first half of Saturday's capital clash, making five key passes in total, albeit while also losing possession 10 times and failing with two of his three dribble attempts.
Spurs went into the break at 1-1 thanks to Dejan Kulusevski cancelling out Mohammed Kudus's opener, and Postecoglou made the bold decision to replace Maddison with Pape Sarr for the second 45 minutes.
There was no indication of an injury to the English playmaker at the time, and sure enough, Postecoglou confirmed in his post-game press conference that he took off Maddison for tactical reasons.
Postecoglou: 'We needed Sarr's running power'
"I just felt West Ham ask you certain questions in midfield areas and I just felt Pape's running power would help us in the second half," football.london quotes Postecoglou as saying.
"They obviously worked hard in the first half and I thought he could give us some real energy. I thought he did really well and he gave us a platform to really threatening every time we want forward and clinical in our football."
The half-time switch more than paid its dividends for Tottenham, as Yves Bissouma propelled the hosts into the lead within seven minutes of the restart, not long before a highly comical Alphonse Areola own goal.
Sarr also justified Postecoglou's faith in him, setting up Son Heung-min for the game's fifth and final goal, as Spurs immediately bounced back from their embarrassing 3-2 collapse against Brighton & Hove Albion before the international break.
The derby briefly descended into chaos at the end, as West Ham goalscorer Kudus left both Micky van de Ven and Richarlison on the deck; replays showed he swiped at the former's face before doing the same to Sarr.
Postecoglou comments on Kudus red and confirms fresh Spurs injury blow
Kudus was initially booked for his part in the melee before referee Andy Madley upgraded his punishment, although Postecoglou was loath to discuss the incident in depth and insisted that the official had control of the situation.
"I think the referee handled it. Players are frustrated out there and I'll let the referees deal with that," Postecoglou added, before also going on to confirm a fresh injury blow for his side.
Djed Spence - who has just signed a new contract with the Lilywhites - was missing from the ranks on Saturday lunchtime, and Postecoglou revealed that he had sustained a groin issue, although he is hopeful that the defender will be back imminently.
"He picked up a bit of a groin strain in training. Hopefully nothing too bad but he missed out today," the Tottenham boss confirmed.
Spurs' thrashing of West Ham lifted them up to seventh in the Premier League table, and the Lilywhites now have four days to rest up before hosting AZ Alkmaar in the Europa League on Thursday evening.